1. Field of the Invention
The present invention relates generally to a converter unit of a camera, and more particularly to a converter unit of a camera, which is capable of adjusting optical axes of converter lenses that are inserted into an optical path of a lens unit of the camera.
2. Description of Related Art
According to a conventional converter unit of a lens unit for a broadcasting TV camera, an external control lever, etc. is operated to insert a converter lens into an optical path of the lens unit to thereby alter the focal length of the lens unit. For example, when a 2.times. extender lens enters the optical path of the lens unit, the focal length of the lens unit is doubled.
Recently, in the field of broadcasting TV cameras, there is a camera capable of selectively switching the aspect ratios between 4:3 and 16:9. In this switchable camera, a charge-coupled device (CCD) of the aspect ratio 16:9 is used for an imaging device. When the aspect ratio is set at 4:3, the right and left areas of the CCD are unused and only the area with the aspect ratio 4:3 at the center is used. Accordingly, the angle of view is reduced by approximately 20%, and the focal length of the lens unit appears to become longer.
To eliminate the above-mentioned disadvantage, it is proposed that an approximately 0.8.times.converter lens, which is called a ratio converter lens, is arranged on the optical path of the lens unit to compensate the focal length of the lens unit when the aspect ratio is set at 4:3.
Moreover, there is a conventional converter unit that is provided with the extender lens and the ratio converter lens to extend the focal length of the lens unit and compensate the focal length on the aspect ratio 4:3. The extender lens extends the focal length of the lens unit whereas the ratio converter lens contracts it. Both the extender lens and the ratio converter lens, however, are converter lenses for altering the focal length of the lens unit, and they are constructed in the same manner.
The applicants have proposed a converter unit that includes two kinds of extender lenses in Japanese Patent Provisional Publication No. 8-171043. According to this converter unit, the extender lenses are revolvably mounted on a single rod in order to simplify the structure, and a desired extender lens is revolved as the need arises and enters and leaves the optical path of the lens unit. One of the applicants has proposed the same in the case that one of the extender lenses is the ratio converter lens in Japanese Patent Provisional Publication No. 9-264077. According to these converter units, the optical axes of the extender lenses are adjusted at the same time by adjusting the direction of the single rod when the extender lenses are inserted into the optical path of the lens unit.
It is, however, difficult to adjust the optical axes of both the extender lenses at the same time by adjusting the direction of the single rod. For this reason, the optical axis of one of the extender lenses that is more sensitive or of a higher magnification is priorly adjusted in the past, but in this case, the optical axis of the other extender lens with the lower magnification (or the ratio converter lens) greatly deviates.